High efficiency solid oxide fuel cell—internal combustion engine hybrid power system

Abstract

A hybrid stationary power generator is provided. The system is fueled from natural gas and based on SOFCs and high efficiency, internal combustion (IC) engine technologies is conceived to generate electric power at 100-kW scale with an efficiency of 71% and a capital cost of <900 $/kW. This novel system integrates a solid oxide fuel cell (SOFC) stack with a high efficiency stationary engine and balance-of-plant (BOP) equipment to create a hybrid power system.

The invention claimed is: 
     
       1. A hybrid power generator system, comprising:
 a solid oxide fuel cell having an anode, an electrolyte layer, an interconnect layer, and a cathode; 
 a fuel line connected to an anode pathway of said fuel cell, wherein said fuel line carries a fuel to said anode pathway, wherein said fuel in said anode pathway reacts at said anode and produces a modified fuel with a composition that is different than said fuel; 
 an oxidizer line connected to a cathode pathway of said fuel cell, wherein said oxidizer line carries a pressurized first oxidizer to said cathode pathway, and wherein said pressurized first oxidizer in said cathode pathway reacts at said cathode and produces a modified first oxidizer with a oxidation composition that is different than said pressurized first oxidizer, and said fuel cell generates electric power from said reactions at said anode and cathode; 
 an internal combustion engine located downstream from said fuel cell having an intake, wherein the internal combustion engine comprises a driveshaft, wherein the driveshaft powers at least one component of the system; 
 a compressor powered by said driveshaft of said internal combustion engine, wherein said compressor intakes a first oxidizer and exhausts said pressurized first oxidizer at a higher pressure; 
 an anode exit line, connecting said anode pathway of said fuel cell to said intake of said internal combustion engine and carrying said modified fuel from said fuel cell to said intake; 
 a cathode exit line, connected to said cathode pathway of said fuel cell; and 
 an oxidizer heat exchanger, connected to said oxidizer line and said cathode exit line, wherein said cathode exit line carries said modified first oxidizer from said fuel cell to said oxidizer heat exchanger. 
 
     
     
       2. The hybrid power generator system of  claim 1 , further comprising:
 a fuel heat exchanger connected to at least one of said fuel line and said anode exit line, wherein said modified fuel in said anode exit line transfers heat to said fuel in said fuel line within said fuel heat exchanger, and said fuel enters said fuel heat exchanger at a first temperature and exits said fuel heat exchanger at a second temperature, wherein the second temperature is greater than the first temperature. 
 
     
     
       3. The hybrid power generator system of  claim 1 , wherein said modified first oxidizer in said cathode exit line transfers heat to said pressurized first oxidizer in said oxidizer line within said oxidizer heat exchanger, and said pressurized first oxidizer enters said oxidizer heat exchanger at a first temperature and exits said oxidizer heat exchanger at a second temperature, wherein the second temperature is greater than the first temperature. 
     
     
       4. The hybrid power generator system of  claim 1 , further comprising:
 a modifier element connected to said anode exit line, wherein said modified fuel enters said modifier element at a first pressure and exits said modifier element at a lower second pressure to generate a pressure differential, wherein said modifier element produces mechanical energy from said pressure differential, and said compressor is at least partially powered by said modifier element. 
 
     
     
       5. The hybrid power generator system of  claim 4 , wherein the modifier element is at least one of a combination of a recycle blower, a mixing valve, and an ejector. 
     
     
       6. The hybrid power generator system of  claim 4 , further comprising a recycle line connected to said anode exit line and to said modifying element, wherein said fuel moving through said modifying element entrains said modified fuel from said anode exit line to heat said fuel. 
     
     
       7. The hybrid power generator system of  claim 6 , further comprising:
 a desulfurizer connected to said fuel line at a location upstream of said modifying element, wherein said fuel enters said desulfurizer with a first sulfur content and exits said desulfurizer at a second sulfur content, and wherein the second sulfur content is less than the first sulfur content. 
 
     
     
       8. The hybrid power generator system of  claim 7 , further comprising:
 a fuel compressor connected to said fuel line at a location upstream of said desulfurizer, wherein said fuel enters said fuel compressor at a first pressure and exits said fuel compressor at a higher second pressure. 
 
     
     
       9. The hybrid power generator system of  claim 1 , wherein said fuel is at least one of a methane, an ethane, a propane, or a butane, and said first oxidizer is air, exhaust air, oxygen rich air, oxygen, or combinations thereof. 
     
     
       10. The hybrid power generator system of  claim 1 , further comprising:
 an electric circuit connected to said anode and to said cathode, wherein said reactions cause ion migration through said electrolyte layer and cause electricity to flow through said electric circuit to generate said electric power. 
 
     
     
       11. The hybrid power generator system of  claim 10 , further comprising an inverter connected to said electric circuit to convert said electric power from direct current to alternating current. 
     
     
       12. The hybrid power generator system of  claim 1 , further comprising:
 a generator connected to the driveshaft of said internal combustion engine, wherein said generator converts at least some of said mechanical power produced by said driveshaft into electric power. 
 
     
     
       13. A method of generating power, comprising:
 providing at least one fuel cell having an electrolyte layer and an interconnect layer positioned between an anode and a cathode; 
 reacting a fuel at said anode to produce a modified fuel with a composition that is different than said fuel; 
 reacting a pressurized first oxidizer at said cathode to produce a modified first oxidizer with a composition that is different than said pressurized first oxidizer; 
 generating electric power, by said fuel cell, based on said reactions at said anode and said cathode and based on a resulting ion migration through said electrolyte layer; 
 providing an internal combustion engine having an intake downstream from the fuel cell; 
 conveying said modified fuel from said anode to said internal combustion engine; 
 generating mechanical power, by said internal combustion engine, by combusting said modified fuel and a second oxidizer; 
 pressurizing, by a compressor, a first oxidizer to said pressurized first oxidizer, wherein said compressor is powered by said internal combustion engine; 
 conveying said modified first oxidizer from said cathode to an oxidizer heat exchanger; and 
 heating, at said oxidizer heat exchanger, said pressurized first oxidizer at a location upstream of said fuel cell using said modified first oxidizer. 
 
     
     
       14. The method of  claim 13 , further comprising:
 heating, at a fuel heat exchanger, said fuel at a location upstream of said fuel cell using said modified fuel, wherein said fuel enters said fuel heat exchanger at a first temperature and exits said fuel heat exchanger at a higher second temperature. 
 
     
     
       15. The method of  claim 14 , wherein said first temperature is between approximately 220° C. and 250° C., and said second temperature is between approximately 510° C. and 740° C. 
     
     
       16. The method of  claim 13 , wherein said pressurized first oxidizer enters said oxidizer heat exchanger at a first temperature and exits said oxidizer heat exchanger at a higher second temperature. 
     
     
       17. The method of  claim 16 , wherein said first temperature is between approximately 180° C. and 220° C., and said second temperature is between approximately 615° C. and 645° C. 
     
     
       18. The method of  claim 13 , wherein an operating temperature of said fuel cell is between approximately 600° C. and 850° C. 
     
     
       19. The method of  claim 13 , wherein an operating pressure of said fuel cell is between approximately 3 bar to 5 bar. 
     
     
       20. A hybrid power generator system, comprising:
 a fuel cell having an anode, an electrolyte layer, an interconnect layer, and a cathode; 
 a fuel line connected to said anode of said fuel cell, wherein said fuel line carries a fuel to said anode, wherein said fuel reacts at said anode and produces a modified fuel with a composition that is different than said fuel; 
 an oxidizer line connected to said cathode of said fuel cell, wherein said oxidizer line carries a pressurized first oxidizer to said cathode, wherein said pressurized first oxidizer at said cathode reacts and produces a modified first oxidizer with a composition that is different than said pressurized first oxidizer, and said fuel cell generates electric power from said reactions at said anode and cathode and from a resulting ion migration through said electrolyte layer; 
 an internal combustion engine having an intake; 
 an anode exit line connecting said anode of said fuel cell to said intake of said internal combustion engine, wherein said anode exit line carries said modified fuel from said fuel cell to said intake, and said internal combustion engine combusts a combination of said modified fuel and a second oxidizer to generate mechanical power; 
 a compressor powered by said internal combustion engine, wherein said compressor intakes a first oxidizer and exhausts said pressurized first oxidizer at a higher pressure; 
 a fuel heat exchanger connected to said fuel line and to said anode exit line, wherein said modified fuel in said anode exit line transfers heat to said fuel in said fuel line within said fuel heat exchanger, and said fuel enters said fuel heat exchanger at a first temperature and exits said fuel heat exchanger at a higher second temperature; 
 a cathode exit line connected to said cathode of said fuel cell; 
 an oxidizer heat exchanger connected to said oxidizer line and to said cathode exit line, wherein said cathode exit line carries said modified first oxidizer from said fuel cell to said oxidizer heat exchanger, wherein said modified first oxidizer in said cathode exit line transfers heat to said pressurized first oxidizer in said oxidizer line within said oxidizer heat exchanger, and said pressurized first oxidizer enters said oxidizer heat exchanger at a first temperature and exits said oxidizer heat exchanger at a higher second temperature; and 
 a combining element comprising a blower and a mixing valve or an expander, connected to said cathode exit line, wherein said modified first oxidizer enters said combining element at a first pressure and exits said combining element at a lower second pressure to generate a pressure differential, and wherein said combining element produces mechanical energy from said pressure differential of said modified first oxidizer, wherein said compressor is at least partially powered by said combining element.